/* Adding the Modulus operator and provision for negative numbers
* Program is given the input in a single and and it print the output upon
* getting a \n character.
* For e.g:
*
* 10 10 + 100 + 2 *
*       240
*/

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>

#define MAXOP 100
#define NUMBER '0'

int getop(char []);
void push(double);
double pop(void);

/* reverse polish calculator */

int main(void)
{
    int type;
    double op2;
    char s[MAXOP];

    while((type = getop(s)) != EOF)
    {
        switch(type)
        {
            case NUMBER:
                push(atof(s));
                break;
            case '+':
                push(pop()+pop());
                break;
            case '*':
                push(pop()*pop());
                break;
            case '-':
                op2 = pop();
                push(pop()-op2);
                break;
            case '/':
                op2 = pop();
                if(op2 != 0.0)
                    push(pop()/op2);
                else
                    printf("error:zero divisor\n");
                break;
            case '%':
                op2 = pop();
                if(op2 != 0.0)
                    push(fmod(pop(),op2));
                else
                    printf("erro:zero divisor\n");
                break;
            case '\n':
                printf("\t%.8g\n",pop());
                break;
            default:
                printf("error: unknown command %s\n",s);
                break;

        }
    }
    return 0;
}


#define MAXVAL 100

int sp = 0;
double val[MAXVAL];

void push(double f)
{
    if(sp < MAXVAL)
        val[sp++]=f;
    else
        printf("error:stack full, cant push %g\n",f);
}


double pop(void)
{
    if(sp>0)
        return val[--sp];
    else
    {
        printf("error: stack empty\n");
        return 0.0;
    }
}

#include<ctype.h>

int getch(void);
void ungetch(int);

int getop(char s[]) {
    int i, c;
    while ((s[0] = c = getch()) == ' ' || c == '\t')
        ;
    s[1] = '\0';
    if (!isdigit(c) && c != '.' && c != '-')
        return c;       // not a number
    i = 0;
    if (c == '-' || isdigit(c))     // collect integer part along with '-'
        while (isdigit(s[++i] = c = getch()))
            ;
    if (c == '.')       // collect fraction part
        while (isdigit(s[++i] = c = getch()))
            ;
    s[i] = '\0';
    if (c != EOF)
        ungetch(c);
    if (strcmp(s, "-") == 0)
        return '-';
    return NUMBER;
}

#define BUFSIZE 100

char buf[BUFSIZE];
int bufp = 0;

int getch(void)
{
    return (bufp > 0) ? buf[--bufp] : getchar();
}

void ungetch(int c)
{
    if(bufp >= BUFSIZE)
        printf("ungetch: too many characters\n");
    else
        buf[bufp++] = c;
}